Cells Of The Nervous System Flashcards
What are the two pairs of the nervous system?
CNS - brain, brain stem, cerebellum, spinal cord
PNS - nerve fibres originating from CNS
What is the structure of the brain?
Two cerebral hemispheres (aka the telencephalon). These consist of gyri and sulci
Each hemisphere is split into four:
Frontal - executive functions such as personality
Parietal - somatic sensory cortex, processes tactile info
Temporal - hippocampus and amygdala, short term memory and behaviour. Wernickes area, auditory perception and speech
Occipital - processing visual info
What does the brain stem consist of?
Midbrain
Pons
Medulla
They control lots of functions eg. Respiration and heart rate. They are the target and source of all the cranial nerves
What does the cerebellum do?
It is attached to the brain stem
Important role in balance, motor coordination and posture
What is the spinal cord?
Exetends down from the medulla
Acts as a conduit for neural transmission but can coordinate some reflex actions
What is a neurone?
Polymorphous, can’t be lassitude on shape, location or structure
A mature Neuron is a non-dividing excitable cell whose main function is to receive and transmit information in the form of electrical signals
What are the main types of morphology for neurone?
- Uni polar - 1 axonal projection
- Pseudo-unipolar - single axonal projection that divides into 2
- Bipolar - 2 projections from the cell body (1 is axon, the other is a dendrite)
- Multipolar - numerous projections from cell body (only one is an axon). Includes: pyramidal cells, purkinje cells, golgi cells
What are some common features of neurons?
The soma (cell body/perikaryon):
Contains nucleus and ribosomes, neurofillaments are important in structure and transport
The Axon:
Long processes (eg. Nerve fibres), originated from soma at the axon hillock. Can branch off into collaterals. Usually covered in myelin
Dendrites:
The highly branched cell body. NOT covered in myelin. Receive signals from other neurones
What are some of the other cell types in the CNS?
Astrocytes: most abundant cell. Structural and play a role in cell repair, synapse formation, neuronal maturation and plasticity
Oligodendrocytes and Schwann cells: oligodendrocytes are the myelin producing cells in the CNS. Schwann Cells do the same in the PNS. Each oligo sends out numerous projections that form internodes of myelin covering the axons of neurons, they can myelinate a number of axons. Each Schwann cell can only myelinate one axon segment
Microglia and ependyma: microglial cells are specialised and similar to macrophages. They carry out the immune functions of the CNS. Ependymal cells are epithelial cells that line the fluid filled ventricles regulating the production and movement of cerebrospinal fluid
What are some of the concentrations making up the resting membrane potential?
Na+ (in: 5-15 out: 140-155)
K+ (in: 140-160 out: 2-5)
Ca2+ (in: 0.1 out: 1-2)
Cl- (in: 5-10 out: 70-140)
All in mM
Cell membrane is impermeable to these. All transportation is regulated by channels and pumps
What is the resting membrane potential?
A result of the concentrations of different ions inside and outside of the cell
The outside is the zero reference point. It has a voltage of 0mV
The inside has a negative membrane potential of around -50 to -90 mV
So the RMP is said to be around -70mV
This allows the cell to become hyperpolarised (more -ve) or depolarised (if enough causes an action potential) (+10mV)
What happens regarding sodium and potassium ions across a membrane during propagation?
At RMP: VGSC and VGKC are closed
At membrane depolarisation:
- VGSC open —> influx of Na+ —> further depolarisation
- VGKC open —> efflux of K+ —> membrane repolarisation
How is the concentration of ions around the cell membrane kept in balance after an action potential?
Na+ - K+ ATPase ( sodium potassium pump)
- In its resting configuration Na+ enters vestibule. Upon phosphorylation the ions are transported through protein
- In active configuration Na+ removed from cell. K+ enters vestibule. Pump returns to resting configuration and K+ is transported back into cell
3 sodium’s out, two patassiums in
What is saltatory conduction?
AP spreads along axon by “cable transmission”
Myelin prevents AP spreading because it has a high resistance and a low capacitance
Nodes of ranvier are small gaps in the myelin sheath
Saltatory conduction is when the action potential jumps between nodes
What does a synapse consist of?
Axon terminal
Synaptic cleft
Postsynaptic cell (dendrite of another axon)
